Aims: The Treatment of Lead-exposed Children Trial (TLC) is a randomized, double-blind, placebo-controlled trial of whether the oral lead chelating drug succimer, given to children with moderate lead poisoning, prevents or reduces lead associated deficits in behavior, cognition, neuropsychological function, and growth. Procedures and techniques: TLC randomized 780 moderately lead-poisoned toddlers to receive either succimer or placebo, and then followed them for 3 years with psychological tests and measurements of their growth. All children received home clean up and vitamin and mineral supplementation. Enrollment of children began in August 1994, and follow-up was completed in about March 2000. Data analysis leading to publication of the main psychological results was finished this year, and the results concerning growth are submitted. Accomplishments: TLC provided direct data that succimer does not produce higher scores on a battery of instruments designed to detect the effects of lead; despite lowering blood lead. It also provided indirect data that any chelation regimen is likely to be ineffective, since no available drug is more efficacious, and implies that primary prevention is the correct public health strategy. Only a formal trial with good power can frame such a negative result convincingly. TLC results showing that drug therapy is not effective for improving cognitive and neuropsychological function in lead-exposed children will reinforce the importance of a national commitment to primary prevention Succimer slowed growth in height and in weight in the 34 months after treatment began. The children given succimer grew 0.25 cm (0.05, 0.45) less in the first 12 months of follow-up, and 0.35 cm ( 0.05, 0.72) less over 34 months follow-up. Children given succimer were also lighter: -0.07 kg (-0.16, 0.01) at 12 months and -0.13 kg (-0.25, -.01) at 18 months, without further declines to 34 months of follow-up.